<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .topBox,
        .bottomBox {
            width: 200px;
            height: 200px;
            border: 1px solid black;
            text-align: center;
            line-height: 200px;
        }
    </style>
</head>

<body>
    <div id="app">
        <div v-show="item" class="topBox">上盒子</div>
        <div v-if="item" class="bottomBox">下盒子</div>
    </div>

    <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>

    <script>
        const app = new Vue({
            el: '#app',
            data: {
                item: true
            }
        });
    </script>
</body>

</html>